The most commonly used material for interventional embolization of intracranial aneurysms is a detachable coil, which is a soft platinum-made wire. During the embolization procedure, a microcatheter is inserted into the aneurysm cavity, and then a push rod is used to push the detachable coil into the aneurysm cavity through the microcatheter.
At present, there are four main ways to detachable coils: hot melt release, electrolytic release, mechanical release and hydrolytic release. Among them, electrolytic release is the longest-developed release method. However, since the metal wires used for electrolytic release are mostly made of stainless steel, it takes a long time to completely release, and the probability of problems such as failure to release is high. The release efficiency and stability are low, and the ideal stable and efficient release effect cannot be achieved. Therefore, other release methods have been developed later.
The electrolytic release of the detachable coil generally involves the positive and negative electrodes of the release device entering the human blood through metal rods or metal needles respectively and then energizing the body. The metal wire used to connect the detachable coil to the positive metal rod is electrolyzed in the blood to become metal ions, and then the metal wire breaks, achieving the release effect. The disadvantage is that after the electric welding cools down, the welding part will be uneven, which can easily generate a higher voltage, making it difficult to control the time it takes to release the detachable coils from the microcatheter.
The hot melt release detachable coil is achieved by melting the connecting section between the push rod and the detachable coil through the heating coil, and the detachable coil is released by melting the thermal fuse when the heat reaches a certain level. This method requires the introduction of current, wires, electrodes, etc., and smoke will be generated during hot melting, which may cause local damage to the human body.
Mechanical release of the detachable coil is achieved through a special mechanical structure and an operating device. The current mainstream method is the ferrule type, that is, a movable connecting rod with a spherical end is used, and its head end is connected to the detachable coil. The release wire and the movable connecting rod are assembled and placed in the delivery catheter together, and the detachable coil is released by withdrawing the release wire.
The hydrolytic coil release system consists of a high-pressure injector, a coil delivery tube and a bare platinum coil. The coil is released by injecting solvent into the delivery tube to dissolve it.